Buck/boost voltage regulator employing shunt magnet amplifier



Sept- 23, 1969 J. A. BASSETT. JR 3, 9, 7

BUCK/BOOST VOLTAGE REGULATOR EMPLOYING SHUNT MAGNET AMPLIFIER Filed Sept. '7, 1967 I VENTOR Ja /v 2 BasszmJg ATTORNEYS United States Patent US. Cl. 323-45 9 Claims ABSTRACT OF THE DISCLOSURE A voltage regulator having a pair of magnetic amplifiers connected in shunt across the supply transformer with a connection between the two magnetic amplifiers and the transformer, said connection having a transformer Winding therein connected in one of the leads to the load so that the direction of current in said connection will provide a bucking or boosting voltage to the load.

This invention relates to alternating current voltage regulators and more particularly to a regulator of the buck-boost type employing magnetic amplifiers or saturable reactors to provide the desired regulation.

A number of voltage regulators for maintaining substantially constant load voltage despite changes in line voltage, load and frequency have been proposed in the past. Some of these have also utilized saturable reactors or magnetic amplifiers as part of the regulating system. Such reactors or amplifiers, as is well known in the art, often control transformer windings which give an airing (boosting) or opposing (bucking) effects to the voltage normally supplied 'by the main transformer winding of the regualtor.

An object of the present invention is to provide a new and improved voltage regulator or voltage regulating system of the above described buck-boost type.

Another object of the invention is to provide a magnetic amplifier voltage regulating system in which the amplifiers are supplied with external feedback proportional to the load.

A further object of the invention is to provide a magnetic amplifier voltage regulating system in which load controlled feedback is supplied directly to the load or gate coils of the amplifiers.

A further object of the invention is to provide a regulating circuit in which the requirement for balancing or matching the magnetic characteristics of the cores of the magnetic amplifiers is obviated.

A still further object of the invention is to provide a regulating system in which a tuned circuit means connected across one of a plurality of magnetic amplifiers provides additional range to the regulator.

In one aspect of the invention, a transformer winding in series with an auxiliary transformer winding provides an output voltage. Connected across the input voltage are two series connected magnetic amplifiers. Connected between a tap on the first mentioned transformer winding and a midpoint of the series connected magnetic amplifiers is a primary for the auxiliary winding. The magnetic amplifiers are provided with DC. bias and control windings, the first of which is connected to a source of DC. current, and the second to a load voltage sensing device. Instead of being self-saturating, however, the extra D.C. saturating or gain current needed for efiicient operation of the magnetic amplifiers is supplied by external feedback transformers connected in the load circuit.

In a second aspect, the gate or load connected windings of the magnetic amplifiers are divided into pairs and 3,469,179 Patented Sept. 23, 1969 each pair is crisscross connected so as to provide a bridge circuit to which the DC. feedback is connected, thereby permitting use of the common windings for both the gate and feedback circuits and obviating the necessity for magnetically balancing the mag-amp cores.

The foregoing and other objects, features and advantages of the invention will become apparent from the following description and accompanying drawing which are merely exemplary.

In the drawing:

The single figure is a schematic wiring diagram of an embodiment of the invention.

Referring to the drawing, there is shown a transformer 10 having a winding 12 which in the illustrated embodiment comprises an autotransformer. The winding 12 is connected across input line terminals 14 and 16 by lines 18 and 20. The line 18 is connected to a conductor 22 leading to the secondary 24 (shown split in the illustrated embodiment) of an auxiliary transformer 26. A conductor 28 connects the secondary 24 to a load line 30 having a load or output terminal 32. The other input line 20 is connected by a lead 34 to a load or output terminal 36.

Two magnetic amplifiers 40 annd 42 are connected in series across the input lines 18 and 20 by leads 44, 45 and 46. The midpoint 48 of lead 45 is connected through a conductor 50 and the primary 52 of auxiliary transformer 26 to a tap 54 on winding 12. Each of the magnetic amplifiers 40 and 42 comprises two cores 60 upon which a pair of coils 62 and 64 are crisscross connected by conductors 66 and 68 to a pair of coils 70 and 72. The coils 62, 64, 70 and 72 are so wound, as indicated by black dots, as to form a bridge having intermediate terminals 74 and 76. The magnetic amplifiers 40 and 42 are provided with series connected DC. bias Windings 78 and 80 and series connected control windings 82 and 84 which are connected by conductors 86, 88, and 92 to suitable sensing, amplification, control and biasing circuitry indicated generally by the box 94.

Included in the lead 46 connected to input line 20 is the primary of a current transformer 102. Also included in the lead 44 connected to input line 18 is the primary 108 of a current transformer 112. The transformer 112 has a secondary 114 provided with terminal leads 116 and 118 passing through diodes 120 and 122 and choke 124 to the terminal 74 of the crosscrossed coils of the magnetic amplifier 40. The secondary 114 of transformer 112 is also provided with a mid-tap connected by line 126 to the crisscrossed terminal 76 of amplifier 40. In like manner, the transformer 102 is provided with a secondary 130 having its terminals connected through diodes 132 and 136 and connector 138 to the terminal 74 of magnetic amplifier 42, and a lead 146 connects the terminal 76 of magnetic amplifier 42 to the midpoint 150 of the secondary 130 of transformer 102 through a choke 152.

Clipper and filter circuits are also preferably provided. As shown in the drawing, the clipper circuit comprises a pair of silicon-controlled rectifiers connected in parallel or full-wave relationship with the box 94 by conductors (not shown) connecting the terminals XX and YY. The silicon-controlled rectifiers 160 are connected across the primary 52 of transformer 26 through a lead 162, winding 52, a winding 164 on the core of transformer 26, lead 166, clipper winding 168 on the core of current transformer 112, and lead 170. One of the filter circuits comprises a third harmonic filter having a pair of parallel connected capacitors 172 and 174 connected in series with a choke 176 across the lines 18 and 50. A second filter circuit for fifth harmonics comprises a capacitor 178 and a choke 180 connected in series across the extension winding 164 of transformer 26 and the line 18.

The operation of the foregoing system is as follows. The input voltage is divided across lines 18 and 20 by the magnetic amplifiers 40 and 42. The voltage thus derived at midpoint 48 is applied to the primary 52 of transformer 26. As the other end of winding 52 is connected to a tap 54 on transformer 10, the voltage at point 48 can be either above or below the voltage at point 54. Thus, the voltage across the primary winding 52 of transformer 26 can vary in magnitude and polarity depending upon the ratio of the divider formed by magnetic amplifiers 40 and 42. This voltage is transferred to the secondary 24 of transformer 26 which is connected in series with the output or load and thus adds to (boosts) or subtracts from (bucks) the input voltage to hold the output voltage at a constant level.

The gain of the system is largely controlled by the current transformers 102 and 112 having their primaries 100 and 108 connected in series with the amplifiers 40 and 42. Due to the crisscrossed bridge connection of the load or gate coils 62, 64, 70 and 72 of these amplifiers, the current from the transformers 102 and 112 can be directly introduced into the gate coils and mixed with the A.C. current flowing therethrough. The chokes 124 and 152 help to control the harmonic content of the divided voltage.

The voltage ratio of the divided magnetic amplifiers 40 and 42 is controlled by the bias and control windings 78, 80, 82 and 84. Current in the control windings 82 and 84 tends to turn magnetic amplifier 40 on and magnetic amplifier 42 off. Bias current through the windings 78 and 80 turns magnetic amplifier 40 off and magnetic amplifier 42 on, the instantaneous polarity of the current through the several control and bias windings being indicated by black dots. The bias windings 78 and 80 are provided with a DC. current which is constant in value. The current through the control windings 82 and 84 is varied by the control circuitry in box 94 which senses the output voltage through lines 190 and 192.

The clipper circuit including the silicon-controlled rectifiers 160 is fired whenever the output voltage exceeds a preset level. Such firing causes the primary winding 52 of transformer 26 to be shorted through extension winding 164, lead 166, winding 168, and lines 170' and 162. This shorting of primary winding 52 is reflected in the secondary 24 of transformer 26. The reflected load current flows in the winding 168 of transformer 112, thereby effecting degeneration of the feedback on magnetic amplifier 40 and ensuring that magnetic amplifier 40 is in an off state when the clipper fires.

The feedback transformers 102 and 112 which control the gain of magnetic amplifiers 40 and 42, respectively do so through DC. current fed into the gate windings 62, 64, 70 and 72 and mixed with the A.C. components through the center tap connections 126 and 146 of diodes 120, 122, 132 and 136. This center tap connection regulates the response time of the system since it provides no low impedance conduction path for DC. when primary current in winding 108 does not flow. The ratio of these transformers is 1:1, providing close to 100% feedback to the magnetic amplifiers, raising the gain so that control current can be extremely low.

It should be noted that the control current flows in both magnetic amplifiers 40 and 42 through windings in series and that this control current turns one magnetic amplifier on While the other is turned off, thereby preventing operation of both magnetic amplifiers at the same time. This ensures a very minimal no load input current. The bridge connections on magnetic amplifiers 40 and 42 provide a crisscrossed connection between the separate magnetic assemblies which obviates the requirement for balancing the two cores, or matching the magnetic characteristics of the two cores.

The capacitors 172 and 174 which are included in the third harmonic filter circuit connected across magnetic amplifier 40 provide at the fundamental frequency a parallel tuned circuit which tends to increase the impedance in this arm of the divider previously described, thus increasing the amount of voltage which can be present across this arm and adding range to the regulator.

What is claimed is:

l. A voltage regulator having input and output terminals, a first transformer winding connected across said input terminals, an auxiliary transformer means connected in series between a terminal of said first transformer winding and one of said output terminals, a connection between a second terminal of said first transformer winding and the other of said output terminals, a pair of series connected variable impedances providing a voltage divider connected in shunt across said first transformer winding and said input terminals, means connecting a winding of said auxiliary transformer means to a midpoint of said series connected variable impedances and an intermediate point of said first transformer winding, and circuit means including a pair of current transformers connected in said shunt circuit means for providing feedback current to said variable impedances.

2. A voltage regulator as set forth in claim 1 in which said variable impedances comprise a pair of magnetic amplifiers.

3. A voltage regulator as set forth in claim 2 in which said magnetic amplifiers include two pairs of gate windings connected in crisscrossed bridge relationship, and said feedback circuit means is connected to said gate windings at the crisscrossed bridge of said windings.

4. A voltage regulator as defined in claim 3 in which said feedback circuit means includes a transformer secondary having terminals connected through diode means to one part of said bridge connection and a center tap connected to a second part of said bridge connection.

5. A voltage regulator as defined in claim 1 in which a clipper circuit including a winding on one of said feedback transformers provides for shorting said auxiliary transformer means upon the output voltage reaching a preset level.

6. A voltage regulator as defined in claim 5 in which said clipper circuit includes a controlled rectifier means. 7. A voltage regulator as defined in claim 1 in which a filter circuit meanshaving capacitance and reactance means tuned to a harmonic of the applied voltage is connected in parallel with one of said variable impedances.

8. A voltage regulator as defined in claim 7 in which a second capacitance and reactance circuit tuned to a different harmonic is connected in parallel with said first filter circuit.

9. The voltage regulator of claim 5 in which said clipper circuit includes an extension winding on said auxiliary transformer and at least one filter circuit.

References Cited UNITED STATES PATENTS 2,714,188 7/ 1955 Scherer 323-66 3,098,193 7/1963 Wallace 323-66 3,201,683 8/ 1965 Hjermstad et al .1 323-45 3,353,093 11/1967 Peterson 323-45 RUDOLPH V. ROLINEC, Primary Examiner MICHAEL J. LYNCH, Assistant Examiner US. Cl. X.R. 

